JPS5852567B2 - Program Denki Yatsuta Cairo - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a programmed electric shutter circuit that allows a camera's shutter speed and aperture to correspond in a certain predetermined relationship to the brightness of a subject.

For a given brightness and film sensitivity used, there are infinite combinations between the shutter speed T and the aperture value A that satisfy the relationship A2/T=fixed.

Therefore, in conventional photographic technology, there is a method of setting either A or T and changing the other so as to satisfy the above conditions.

However, in these cases, one must be set, so it cannot be said that the camera's operation is completely automatic.

Therefore, there is also a so-called programmed shutter method which combines T and a large A and maintains a certain relationship between them while increasing T and decreasing A as the brightness decreases.

Mechanically implementing this method requires a fairly complex mechanism.

It is conceivable to carry out such program control in the electric shutter circuit, but there are problems in that there is a high possibility that mechanical elements will intervene and that the degree of freedom in design will be reduced.

Name of the invention: TTL photometric exposure control device
9035) shows a TTL photometry type shutter-priority exposure lateral movement exposure control device.

The specification and drawings disclose an embodiment in which automatic exposure control using a program control method in addition to aperture priority and shutter priority using the TTL photometry method is disclosed.

It is advantageous in that it can implement a variety of methods, but the control sequence is separate or sequential, such that one is determined before the other.

SUMMARY OF THE INVENTION An object of the present invention is to provide a programmed electric shutter circuit in which the aperture value and shutter speed are determined simultaneously within the same negative feedback system.

The basic structure of the programmed electric shutter circuit according to the present invention will be explained with reference to FIG.

In this program shutter circuit, the aperture value setting means A sets the aperture value.

The feedback voltage generating means B works in conjunction with the aperture value setting means A to generate a feedback voltage corresponding to the aperture value.

The first arithmetic circuit C is an arithmetic circuit that outputs a voltage that is the sum of the feedback voltage and a voltage obtained by logarithmically compressing the photocurrent corresponding to brightness.

The subtraction circuit is formed from a resistor group and an operational amplifier.

The feedback voltage generated by the feedback voltage generating means B and the output voltage of the first arithmetic circuit C are connected to its input terminal.

The input terminal of the differential amplifier E is connected to the output voltage of the subtraction circuit and the feedback voltage.

The differential amplifier E, the aperture value setting means A, and the feedback voltage generating means B constitute a servo mechanism.

The differential amplifier E generates an output for driving the aperture value setting means A so that both input voltages thereof become equal.

The shutter speed control device F is a control device that controls the shutter speed in response to the output of the first arithmetic circuit C.

Due to the operation of the servo mechanism, the differential amplifier E is balanced, so that the aperture value setting means A sets an aperture value corresponding to the brightness, and the aperture value corresponds to the output of the first arithmetic circuit C in that state. Then, the shutter control device F operates, and a shutter speed that provides appropriate exposure for the brightness and aperture value in that state is obtained.

FIG. 2 is a circuit diagram showing an embodiment of a programmed electric shutter circuit corresponding to the basic configuration described above.

In the figure, M12M22M3 and M4 are operational amplifiers.

The operational amplifier M1 is an operational unit forming the first operational amplifier circuit C, and a photovoltaic cell D1 is connected between its input terminals.

This photovoltaic cell D1 is always operated in a state where the terminal voltage is zero by a feedback circuit which will be described later.

A transistor Tr is connected to the non-inverting input terminal of the operational amplifier M1.
The emitter of 2 is connected to the transistor, and the voltage E6 is connected to the base of the transistor.

The output of the operational amplifier M1 is fed back to the input side via the switch SW1, and the output at that time is a feedback voltage E6, which will be described later.
The output voltage is the sum of the voltages obtained by logarithmically compressing the brightness, and the current is obtained by logarithmically expanding the sum.

The switch SW1 is opened in synchronization with the opening of the shutter, and the capacitor C1 is inserted into the feedback circuit.

The inverting input terminal of the operational amplifier M1 has a transistor T whose collector is commonly grounded with the transistor Tr2.
The emitters of r, are connected.

The base voltage EA of the transistor Tr1 is provided by a voltage divider vR1 connected between ground and the voltage Ec1.

The output terminal of the operational amplifier M1 is connected via a resistor R1 to an inverting input terminal of a second operational amplifier M2 included in the subtraction circuit and an inverting input terminal of an operational amplifier M4 forming a comparator of the shutter control device F. It is connected.

The non-inverting input terminal of the operational amplifier M2 of the subtraction circuit is connected to a point P in the feedback circuit via a resistor R3 and to a ground point via a resistor R4.

The output terminal of the operational amplifier M2 of this subtraction circuit is connected to the inverting input terminal of the operational amplifier M3 constituting the differential amplifier E.

It can be understood that the subtraction circuit including the operational amplifier M2 operates qualitatively as follows.

In other words, the subtraction circuit is a circuit that determines how much the motor milk, which is the aperture setting means A, should be moved in response to the brightness of the subject, that is, what value the aperture should be set as a result. .

This subtraction circuit is connected to the operational amplifier M that constitutes the differential amplifier E.
3 In cooperation with the motor M, only a certain proportion of the voltage corresponds to the brightness of the object.

This is to drive the motor.

A motor M is connected to the output terminal of the operational amplifier M3 that constitutes the differential amplifier E.

is connected. This motor Mo has an operational amplifier M3
The output terminal of the variable resistor connected to the non-inverting input terminal of M is adjusted to adjust the divided voltage E5,
It functions to balance the inputs of 3.

A voltage ETr that determines the trigger level is applied to a non-inverting input terminal of an operational amplifier M4 used as a comparator of the shutter speed control device F.

The output terminal of operational amplifier M4 is connected to the base of transistor T r 3 via resistor R5.

The electromagnet Mg connected to the collector of the transistor Tr3 is conductive until the inverting input of the operational amplifier M4 reaches ETr, and when it reaches ETr, it becomes non-conductive and functions to close the shutter.

If the photocurrent generated by the photovoltaic cell D1 is IL, the base-emitter voltage E2 of the transistor Tr2 is given by the following equation.

R2-(kT/q) ・I n (IL/Is)
--・■Here L・te, k: Boltzmann constant T: Absolute temperature (0K) q: Electron charge Is:) Saturation current between the base and emitter of transistor Tr2 The photovoltaic cell operates with a voltage of 0 volts between the terminals. Therefore, in the circuit shown in FIG. 2, the following relationship holds true.

E1+EA-E2+E6 ・・・・・・・・・・・・・・・
...■The following relationship holds between the base-emitter voltage of El in the above equation, that is, the transistor Tr, and the current ■1.

However, it is assumed that transistors Tr1 and Tr2 have the same characteristics.

11=Is −exp (qE1/kT) −・−
From the formula ■■, E = E2 + E6 - EA, so the formula ■ becomes as follows.

11-■5-expq(E2+E6-EA)kT...
...The current 11 is given by the following equation from the equations ■'■ and equations ■'.

Ii ””It, 'exp(1(Ea EA)
/kT ・-(1) In other words, the current ■1 flowing in the feedback circuit of the operational amplifier M1 reduces the photocurrent IL to eXp(1(R6-
EA)/kT times the current.

This current 11 is a current that determines the shutter speed, and it can be seen from the Jy equation that it is dependent on R6, which is determined within the EA circuit system, which is set by the voltage E2 and VRt, which correspond to brightness.

①In the formula, 11 is the photocurrent E6. It shows that it is subordinate to EA.

Next, consider R6.

Since the amplification system of the operational amplifier M1 of the first operational circuit C satisfies the above formula 0, when the conditions of R1=R2 and R3=R4 are given to the resistor group in the subtraction circuit, the operational amplifier M2 Since the amplification factor is 1, E, =E6-E3=E6-(E2+E6)=-R2・
・－・・・■Also, as mentioned above, motor M.

Since R5 is adjusted so that the input voltage of operational amplifier M3 becomes equal, R4 and E become equal in the steady state.

R4-E, ・・・・・・・・・・・・・・・・・・
. . .■ Also, assuming that R6 and R7 have the same resistance R, R6 is given as the average value of R5 and EB.

Note that the resistance values of resistors R3 and R4 are sufficiently larger than those of resistors R6 and R7, and VB2. It is assumed that the resistance value of VB2 is sufficiently smaller than that of resistors R6 and R7, and that the base current of transistor Tr2 can be ignored.

E6= (E5+EB)/2 ・・・・・・・・・
...■ Also, from the formula of ■■, E6 = (-E2 + EB) / 2 ......
...■From these relationships, the ■expression can be written as follows.

EA+E1=E2+(-E2+EB)/2,'', E1=
E2-E/2 + (EB/2-EA)...
...■The meaning of this expression can be understood as follows.

El on the left side corresponds to the shutter speed, the first term R2 on the right side is determined by the photocurrent, so it corresponds to brightness, and the second term E2/2 on the right side corresponds to the aperture value determined by the calculation of the circuit. Then, if the first term on the right side of the voltage E2 generated in response to the light incident on the light receiving element D1 is determined, the third term on the right side can be considered a constant, so the second term related to the aperture value is unique. Determined by

In other words, 1/2 times the increment of E2 is transmitted as the aperture information increment**.

These relationships are specifically shown in Table 1 in association with brightness (EV).

Madashi e=cT1n 1. /Is volts (C is a proportionality constant) E B / 2 EA-22, 5e.

The relationship between the aperture F and the shutter speed shown in Table 1 is shown in FIG. 3 as a straight line ■.

The slope of this straight line can be set arbitrarily.

In the embodiment circuit configured as described above, the power is first turned on, calculations are performed, and the motor M is turned on.

When the position of VRa is determined by, it is fixed at this position and E5 is determined.

Next, when the switch SW1 is opened in synchronization with the opening of the shutter, charging of the capacitor C1 is started.

If this time elapsed is T, the condenser※※suC1 The terminal voltage Ec of is given by the following equation.

Ec = (11+I (,)・(T/C1')・
...[Phase] When the terminal voltage Ec of the capacitor reaches the trigger level setting voltage ETr of the operational amplifier M4 forming the comparator, the operational amplifier M4 operates to cut off the current of the magnet Mg and close the shutter. .

Replace Ec in the [phase] equation with E'rr, and in the [phase] equation, the light amount IL-T is C1・ETr as exp q
It shows that it is given as divided by (Ea - EA)/kT.

If (Ea EA) is proportional to the absolute temperature T, then LT is always constant.

Therefore, the power supply Ec1 that influences R6 and EA is configured as a power supply whose voltage varies in proportion to the absolute temperature.

In the above embodiment circuit, when the position of the output terminal VB2 of the feedback voltage generating means B is determined and fixed, the aperture value and shutter speed are simultaneously determined.

As is clear from the above description, the programmed electric shutter circuit according to the present invention has an extremely simple configuration, and when the entire system is stabilized, it simultaneously obtains the combination of aperture value and shutter time to provide proper exposure. be able to.

This combination can be arbitrarily selected by adjusting the circuit elements R6 and R7.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the basic configuration of a programmable electric shutter circuit according to the present invention, FIG. 2 is a diagram showing an implementation section of the programmable electric shutter circuit according to the present invention, and FIG. 3 is a graph showing program characteristics. . A... Aperture value setting means, B... Feedback voltage generation means, C... First arithmetic circuit, D...
...Subtraction circuit, E...Differential amplifier, F...
...Shutter speed control device, Ml, M2. M3.
M4... operational amplifier, Mg... release magnet, Trl, Tr2. Tr3...
Transistor, MO...--Motor, vRl)
``R2, VB2... Voltage divider.

Claims (1)

[Claims] 1. An aperture value setting means, a feedback voltage generation means that generates a feedback voltage corresponding to the aperture value in conjunction with the aperture value setting means, and a voltage obtained by logarithmically compressing the photocurrent corresponding to the feedback voltage and brightness. a first arithmetic circuit that outputs a sum voltage; a subtraction circuit that includes a resistor group and an operational amplifier and receives the feedback voltage and the output voltage of the first arithmetic circuit; a differential amplifier which receives a feedback voltage as an input, forms a servo mechanism with the aperture value setting means and the feedback voltage generation means, and generates an output that drives the aperture value setting means so that both input voltages become equal; a shutter speed control device that controls a shutter speed in accordance with the output of the first arithmetic circuit, and when the differential amplifier is balanced, an aperture value corresponding to the distance is set, and in that state. The program is characterized in that the shutter control device operates in response to the output of the first arithmetic circuit to obtain a shutter speed that provides appropriate exposure for the brightness and aperture value in that state. Electric shutter circuit.